Patent GB-168189-A (GB)
Title: Improvements in weighing machines or scales
IPC: G01G1/38
Filed: 1920-06-14
Abstract: 168,189. Imray, O., (Boston Scale & Machine Co.). June 14, 1920. Sliding-weight apparatus.- Relates to a weighing-machine, more particularly of the kind described in Specification 145,044 wherein a poise is moved automatically along a beam by an electric motor to a position beyond the balance point and then back to the balance point by a slow stepby-step movement. The invention consists in supporting the electric motor independently of the beam and utilizing an escapement mechanism to check the action of the motor so as to give the poise the step-by-step movement near the balance point. The change in the direction of the movement of the poise is effected by a reverse switch, which changes the direction of rotation of the motor. The motor drives the poise through a universal joint having conical pivots and connected to a poise shaft mounted on the beam. A weightindicator and a printing-unit are incorporated in the apparatus. A weighing operation is started by turning a key-controlled locking-device 1, Fig. 3, which switches on the current at contacts 7, 9. The reverse switch E is energized and rocks its switches 14, 23 so that the current thus directed through the poise motor D tends to move the poise inward to give an initial tilt to the beam, this movement being prevented however by a latch 93. When a beam lock H is afterwards released, this circuit is broken and another circuit through the reverse switch is substituted. The rotation of the unlocking-device 1 also lights a lamp L to illuminate the weightindicator J, and sounds an electric bell M. Owing to the rotation of the locking-device 1, a starting handle Q may now be turned to the left and perform a series of mechanical operations, namely (1) release the beam lock H and a beam-locating device I, (2) close an indicator shutter K, (3) move a clutch O thus unlocking the poise screw shaft and connecting it to the poise motor D, (4) open switches 37, 49 in the circuit of the reverse switch, lamp and bell, (5) close switches T, 77. A lock dog 59 holds the starting-handle in its new position and also causes contacts 79, 81 in the starting-circuit to be closed. This circuit energizes a magnet 91 and withdraws the catch 93 from an escapement-wheel 95, thus permitting the motor P to traverse the poise B inwards. The opening of the beam lock H closes contacts 97, 99, and the current to the reverse switch E. is directed through mercury cups 101, 107 cooperating with needle contacts on the beam, the switches 14, 23 of the reverse switch being then held in the position for supplying current to the poise motor D to produce inward movement of the poise. When the beam tilts upwards, the needles 103, 105 break the circuit of the reverse switch E and a spring rotates its switches 14, 23 so as to reverse the current through the poise motor and cause the poise to travel rapidly and continuously outwards to a position beyond the balance point. The beam tilts downwards and the needle contacts 103, 105 again energize the reverse switch E, causing the poise motor again to move the poise inwards. This movement takes place in rapid steps controlled by the escapement 95 and by a make-and-break escapement switch 157. The beam presently rises and withdraws the contact needle 163, whereupon the circuit for the escapement switch 157 is deviated through a mercury cup 189 and through a timer switch G, which is arranged to make and break the current through the escapement switch 157 and thus retard its operation so that the poise B is moved slowly inward step-by-step to the balance point. To avoid excessive overtravel of the poise during its outward movement, a weight 224 assists in depressing the beam, but is automatically removed by a motor 224f when the inward movement of the poise commences. After the balancing point is reached, the final movement of the timer switch G (retarded by a fan to produce a pause at the balancing point) bridges contacts 229, 231 and energizes an electromagnetic switch 228 which closes the beam lock H upon the beam and also unlocks the operating- handle Q. The c'osure of the beam-lock lights the lamp L, sounds the bell M, and by means of a trip motor 233 breaks the starting-circuit at the contacts 79, 81. The indicator J is driven by the poise motor in unison with the poise. The printing-mechanism is set by the movements of the indicator, and the platen of the printing- mechanism is actuated by the starting-handle Q when it is moved to the right after the completion of a weighing operation. The handle also opens the switch T, opens the shutter K revealing the indicator reading, closes the beam-locating device I, opens the clutch O, and locks the poise shaft against rotation. If the step-by-step movement is unduly prolonged, due for example to external shocks on the machine, a disc in the escapement throws the escapement out of action and the rapid continuous feed is resumed. The indicator may be adjusted by the poise motor independently of the poise to allow for tare or for alteration in the weight of the platform due to dirt or wear, by applying a key to a slotted locking-device which controls a switch 43 governing the movements of the poise motor. The indicator J, Figs. 30 and 31, comprises a series of number-wheels and is driven from a pinion 419 fast on the same shaft 413 as the units wheel 411. The units wheel carries a disc 427 and a two-toothed plate 421 which at each revolution imparts movement to pinions 423, 429, 441, 445 and to the tens wheel. A star wheel 426 engaging the disc 427 prevents rotation of the pinion 423 except at the moment of transfer. A curved friction clutch 435 yields endways to sudden movement but afterwards returns and picks up the lost movement under the influence of a spring 447. The transfer to the higher numberwheels is similarly effected but without the use of the friction clutch.